The present invention relates to the three-dimensional imaging arts. It particularly relates to the imaging, tracking, and displaying of neural fibers and fiber bundles by diffusion tensor magnetic resonance imaging (DT-MRI), and will be described with particular reference thereto. However, the invention will also find application in conjunction with the tracking and graphical rendering of other types of structures as well as with other imaging modalities such as single photon emission computed tomography imaging (SPECT), computed tomography (CT), positron emission tomography (PET), and the like.
Nerve tissue in human beings and other mammals includes neurons with elongated axonal portions arranged to form neural fibers or fiber bundles along which electrochemical signals are transmitted. In the brain, for example, functional areas defined by very high neural densities are typically linked by structurally complex neural networks of axonal fiber bundles. The axonal fiber bundles and other fibrous material are substantially surrounded by other tissue.
Diagnosis of neural diseases, planning for brain surgery, and other neurologically related clinical activities as well as research activities on brain functioning can benefit from non-invasive imaging and tracking of the axonal fibers and fiber bundles. In particular, diffusion tensor magnetic resonance imaging (DT-MRI) has been shown to provide image contrast that correlates with axonal fiber bundles. In the DT-MRI technique, diffusion-sensitizing magnetic field gradients are applied in the excitation/imaging sequence so that the magnetic resonance images include contrast related to the diffusion of water or other fluid molecules. By applying the diffusion gradients in selected directions during the excitation/imaging sequence, diffusion weighted images are acquired from which apparent diffusion tensor coefficients are obtained for each voxel location in image space.
Fluid molecules diffuse more readily along the direction of the axonal fiber bundle as compared with directions partially or totally orthogonal to the fibers. Hence, the directionality and anisotropy of the apparent diffusion coefficients tend to correlate with the direction of the axonal fibers and fiber bundles. Using iterative tracking methods, axonal fibers or fiber bundles can be tracked or segmented using the DT-MRI data.
However, fiber tracking results are difficult to interpret by doctors, clinicians, and other medical personnel. Axonal fiber bundles of interest are frequently located in the brain or other regions with very high nerve tissue densities. The tracked fiber typically overlaps, intertwines, crosses, or otherwise intermingles with other fibers/fiber bundles or other small anatomical structures. The relationship of the tracked fiber with the surrounding anatomy including other neural tissues can be an important aspect of the clinical analysis. Hence, there is a need for an improved image representation method and apparatus that emphasize selected features of the tracked fiber while placing the tracked fiber into context with the surrounding anatomy.
The present invention contemplates an improved apparatus and method which overcomes the aforementioned limitations and others.
According to one aspect of the invention, an imaging method is provided for imaging a subject including anisotropic structures. A three-dimensional apparent diffusion tensor map of at least a portion of the subject including at least some anisotropic structures is acquired. The apparent diffusion tensor at a voxel is processed to obtain eigenvectors and eigenvalues. A three-dimensional fiber representation is tracked using the eigenvectors and eigenvalues. The three-dimensional fiber representation is rendered as a hyperstreamline representation. A background image representation is generated. A human-viewable display is produced, including the hyperstreamline representation superimposed on the background image representation.
According to another aspect of the invention, an apparatus is disclosed for tracking fibrous structures in a subject. A magnetic resonance imaging scanner is configured to acquire diffusion-weighted imaging data. A reconstruction processor reconstructs the acquired diffusion-weighted imaging data into diffusion-weighted image representations. A diffusion tensor mapping processor constructs a diffusion tensor map by selectively combining selected diffusion-weighted image representations. An eigenvalues/eigenvectors processor obtains eigenvalues and eigenvectors of the diffusion tensor corresponding to a voxel. A voxel in the fiber tracking process can be substantially smaller than the acquired voxels. A fibrous structure tracking processor computes a fibrous structure representation based on the eigenvalues and eigenvectors and at least one starting voxel selection. A rendering processor computes a hyperstreamline representation of the fibrous structure representation. A display device displays the hyperstreamline representation in a human-viewable medium.
According to yet another aspect of the invention, an imaging method is provided for imaging a subject including fibrous structures. Diffusion tensor magnetic resonance imaging data of the fibrous structures is acquired. The diffusion tensor magnetic resonance imaging data is processed to extract a three-dimensional fiber representation of the fibrous structures. The three-dimensional fiber representation is rendered as one of: a tube with a circular cross-section having a diameter dimension; a tube with an elliptical cross-section having major and minor axis dimensions and an orientation dimension; a ribbon or helix having width and orientation dimensions; and a double ribbon or double helix including a first ribbon having first width and orientation dimensions and a second ribbon having second width and orientation dimensions.
One advantage of the present invention resides in its speed in determining fiber trajectories.
Another advantage of the present invention resides in providing intuitive graphical representations of tracked fiber image parameters that facilitate clinical interpretation and visualizing fiber orientation, diffusion tensor direction, anisotropy, and anatomical orientation.
Yet another advantage of the present invention resides in improved and intuitive color encoding that relates the tracked fiber direction with anatomical orientation.